DESCRIPTION: The long term goal of this research is to provide a genetic framework for understanding the physiological responses of bacteria growing in surface biofilms. These responses have a large impact on our ecology and our health. Our model system is the surface-induced swarmer cell differentiation response discovered in our laboratory in E. coli and S. typhimurium, and known to be elicited by several flagellated bacteria. Swarmer cells are generally long and multinucleate, always hyperflagellated, and can move rapidly over the agar surface in a coordinated manner. There is evidence that the differentiated swarmer-cell stage of some bacteria facilitates pathogenic associations with host tissue. Almost nothing is known about the molecular signaling mechanism of surface sensing. In organisms in which swarming motility has been studied in some detail, the chemotaxis system has been shown to play an important role. The specific aims of this proposal are to understand the mechanism by which the chemotaxis components participate in surface signal transduction, which eventually turns on swarmer cell-specific gene expression. We believe that understanding the genetic basis of swarming in such well-characterized bacteria as E. coli and S. typhimurium will provide valuable clues to understanding surface-specific behaviors in other microorganisms.